A developer composition for a lithographic printing plate provided with a coated layer composed of a photosensitive polymer having in the main chain thereof groups of formula (I) ##STR1## wherein X and Y independently represent hydrogen, halogen, cyano or nitro, and n is an integer of 1 or 2, comprising ethylene glycol monophenyl ether and at least one acid selected from the group consisting of a mineral acid, an organic carboxylic acid and an organic sulfonic acid.